The concept behind this is something quite simple which was previously implemented in grsecurity (check out GRKERNSEC_PROC_ADD) by spender. Almost anyone who has ever developed a kernel heap exploit for the Linux kernel knows that using ‘/proc/slabinfo’ you can easily track the status of the SLAB you are corrupting.
This patch limits the reliability of Linux kernel heap exploitation since unprivileged users can no longer read this PROCFS file.

@puppykitten: As Matt Mackall commented. It got rejected because they believe that it’s just an unimportant limitation against heap exploitation and it forces any legit operation requiring slabinfo to be run as root. Read the follow-up discussion as Matt Mackall said.